In connection with the development of proposed new electronic telephone sets, particularly sets of universal, as nearly world-wide applicability as is feasible, it is desirable to provide a versatile, low-power, microcomputer-controlled set having many special features not included in present standard telephones. Certain features and systems involved in the proposed new electronic telephone set are disclosed in my earlier filed, copending applications listed below (herein incorporated by reference):
Case 1: Ser. No. 67,080, filed Aug. 16, 1979, "Tone Ringing Circuits for Telephone Sets";
Case 2: Ser. No. 72,252, filed Sept. 4, 1979, "Circuits and Methods for Initializing the Loop Current of a Telephone Set";
Case 3: Ser. No. 86,024, filed Oct. 17, 1979, "Speech Networks for Telephone Sets."
In connection with the development of such telephone sets, it is desired to provide improved circuits for storing the last number dialed (LND) in temporary memory (RAM) and for redialing the stored number by operation of an LND redial key included in the dial pad, such LND redial circuits being generally well known in the art. It is further desirable to provide systems for separately storing both the last number dialed and one or more previously dialed numbers, and for selectively redialing any of the stored numbers, at the option of the user, by activation of a corresponding one of two or more redial keys. In connection with the development of a set powered solely from the central office line current, and having no local power source, it is particularly desirable to provide systems for storing previously dialed numbers for an extended time after hanging up the phone, preferably for a time of at least eight hours. It is also desirable to provide improved circuits for single-button dialing of a few permanently stored numbers, such as "Police," "Fire," etc., such systems being generally well known in the art.